Determination of endometrial receptivity toward embryo implantation

ABSTRACT

Methods for detecting receptivity of mammalian endometrium to embryo implantation comprising obtaining a sample of the endometrium, contacting the endometrium with a monoclonal antibody for β 3  and detecting β 3  in the endometrium. The invention also provides for methods of diagnosing infertility in a mammal and methods of detecting the window of embryo implantation in endometrium. Methods of in vitro fertilization, methods of preventing embryo implantation and a method of monitoring endometrial maturation are also within the scope of the present invention. The present invention is also directed to contraceptives. Diagnostic kits useful in the practice of the methods of the invention are also provided.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 09/149,183, filed Sep. 8, 1998, now U.S. Pat. No. 6,733,979, which is a continuation of U.S. application Ser. No. 08/756,211, filed Nov. 25, 1996, now abandoned, which is a divisional of U.S. application Ser. No. 08/400,270, filed Mar. 3, 1995, now U.S. Pat. No. 5,578,306, which is a continuation of U.S. application Ser. No. 08/126,063, filed Nov. 1, 1993, now abandoned, which is a divisional of U.S. application Ser. No. 07/987,706, filed Jun. 12, 1992, now U.S. Pat. No. 5,279,941. Benefit of priority under 35 U.S.C. §120 to each of the above-noted applications is claimed.

REFERENCE TO GOVERNMENT GRANTS

This work was supported in part by research grants from the Biomedical Research Support Grant Program, Division of Research Resources, the National Institutes of Health, grant number B.R.S.B. S07-RR-05415-29. The United States Government may have certain rights in this invention.

BACKGROUND OF THE INVENTION

Over the past decade, investigators have come to recognize the importance of the extracellular matrix (ECM) in directing the growth, differentiation and function of the overlying epithelium. Getzenberg et al., “The Tissue Matrix: Cell Dynamics and Hormone Action”, Endocrine Rev., 11:399-417 (1990). The interaction between cell and extracellular matrix (or substratum) is mediated by several classes of cell adhesion molecules, one of the most important being the integrins. Albelda et al., “Integrins and Other Cell Adhesion Molecules”, FESEB J., 4:2868-2880 (1990). Buck et al. “Integrin, a Transmembrane Glycoprotein Complex Mediating Cell-Substratum Adhesion”, J. Cell Sci. Suppl., 8:231-250 (1987). This diverse family of glycoprotein receptors is expressed on the cell membrane as heterodimeric α and β subunits and is involved in both cell-cell and cell-substratum adhesion. Specific recognition and binding of extracellular matrix (ECM) components such as fibronectin (FN), laminin (LM) and collagen (Col) transmit information to the cytoskeletal structure, an interaction which may have major roles in promoting hormone responsiveness and genomic activation. Burridge et al., “Focal Adhesions: Transmembrane Junctions Between the Extracellular Matrix and the Cytoskeleton”, Ann. Rev. Cell. Biol. 4:487-525 (1988) and Getzenberg et al. supra.

Although extensive information exists about specific integrin proteins, for example, Hemler, M. E. “VLA Proteins in the Integrin Family: Structures, Functions and Their Role on Leukocytes”, Annu. Rev. Immunol: 365-400 (1990), little is known concerning the distribution of these receptors in the female reproductive tract. In the uterus, the endometrium, composed of glandular epithelium and associated mesenchyme (stroma), maintains complex temporal and spatial functions in response to the cyclic hormonal milieu. The search for morphological or biochemical markers for uterine receptivity has been unsuccessful to date as reported by Rogers and Murphy, “Uterine Receptivity for Implantation: Human Studies”, in Blastocyst Implantation, Yoshinaga, K. ed., Serono Symposia, pp. 231-238 (1989). Once such markers are identified, their role in endometrial phenomena including embryo implantation, fertility, contraception and endometrial maturation and receptivity can likely also be identified. Thus, as some integrins appear to meet the criteria for markers of receptivity there is a great need for methods of detecting integrin cell adhesion molecules in endometrium.

SUMMARY OF THE INVENTION

The present invention is directed to methods of detecting receptivity of endometrium to embryo implantation by detecting the β₃ subunit of the α_(v)/β₃ integrin in endometrium with a monoclonal antibody.

Methods of diagnosing fertility and methods of monitoring endometrial maturation in a mammal are also provided by monitoring the appearance of the β₃ subunit of integrin in endometrium from a plurality of stages of the endometrial cycle. This is preferably done with a monoclonal antibody.

The present invention also provides methods of detecting the optimal window of embryo implantation in the endometrium by detecting the β₃ subunit of integrin in an endometrial sample, preferably with a monoclonal antibody.

Further aspects of the invention include methods of preventing embryo implantation by contacting the β₃ subunit of integrin in the endometrium with neutralizing Fab antibody fragments to β₃. Methods of in vitro fertilization are also embodiments of the invention. These comprise detecting the β₃ subunit of integrin in an endometrial sample, fertilizing an egg in vitro, and introducing the zygote into the uterus having endometrial tissue expressing the β₃ subunit.

Contraceptive and diagnostic kits are also contemplated hereby.

These and other aspects of the invention will become more apparent from the following detailed description when taken in conjunction with the following figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1F depict immunoperoxidase staining of normal endometrium. The photomicrographs depict the pattern of distribution for six different integrins that do not appear to change throughout the mentrual cycle. Dark areas represent positive staining, light areas represent absence of stain (absence of specific integrin subunit). Immunohistochemical staining of the collagen/laminin receptor subunits: α₂(A), α₃(B), α₆(C), and β₄(D) shows prominent staining of epithelium (←) and microvessels (←) without significant stromal staining (*) for α₂, α₃, and β₄. Note basolateral staining α₆ and basal staining for β₄. Staining for fibronectin receptor subunits α₄(E), α₅(F) show predominant mesenchyme staining (*) with decreased epithelial staining (←). The immunoreactions (areas of dark staining) were developed by avidin-biotin-peroxidase complex using diaminobenzidine as a chromogen. For greater sensitivity, no counterstain was applied. Magnification: 125×.

FIGS. 2A to 2C show photomicrographs of the immunohistochemical staining for the integrin subunit α₁ in proliferative vs. secretory endometrium. The staining in the glandular epithelium (←) was largely absent in the proliferative phase (A), and pronounced in all sections after menstrual cycle day 14 (B; day 20 endometrium). The microvasculature (←) staining was also pronounced, and did not change throughout the menstrual cycle. The staining noted in secretory endometrial glands was significantly higher than that of background (C). Magnification: 125×.

FIGS. 3A to 3D exhibit immunostaining of α_(v) and β₃ (the two pairing subunits of the vitronectin receptor integrin) in proliferative phase vs. secretory phase endometrium. The staining intensity of α_(v) in the proliferative phase (A) was judged as “+” for the stromal cells (*) and “±” for glandular α_(v) (←). Immunostaining for α_(v) in day 22 endometrium (B) demonstrates a significant increase in glandular staining (example of “++” staining intensity). Likewise, the staining for β₃ was absent in proliferative epithelium (C; ←) and was notably increased in this day 22 secretory endometrium (D). Magnification: 125×.

FIGS. 4A and 4B show relative intensity of staining for the epithelial α_(v) and β₃ subunits in 35 endometrial samples throughout the menstrual cycle. The pattern of expression for α_(v) is shown in A, shows a gradual increase in staining throughout the menstrual cycle. In contrast, the pattern for β₃ in B, shows a more abrupt rise in this integrin subunit around day 20 of the menstrual cycle. Samples were staged according to the last menstrual cycle. Sections were assigned a score of 0 (−; negative), 1 (±; weak), 2 (+; moderate) or 3 (++; strong), by a blinded observer, and confirmed by a second observer.

FIGS. 5A to 5C depict staining intensity of epithelial β₃ in 12 infertility patients with delayed endometrial maturation. Endometrium was collected from women undergoing evaluation for infertility. The biopsies were separated into two groups based on the correlation between histologic criteria and the menstrual cycle dating based on the time of ovulation and/or the subsequent menstrual period. Patients with endometrial biopsies 3 or more days “out of phase” (OOP group) were compared with 25 endometrial biopsies that were “in phase” (Normal) and shown in A. Sections were assigned a score of 0 (−; negative), 1 (±; weak), 2 (+; moderate) or 3 (++; strong), based on the intensity of epithelial β₃ staining. Examples of immunohistochemical staining of an “out of phase” biopsy (B) and a normal “in phase” sample (C) is included to contrast the epithelial β₃ staining in each group. Magnification: 400×.

FIGS. 6A to 6D exhibit immunoblot analysis of proliferative and secretory endometrium, stained for the β₃ subunit. (A) Immunoblot of platelet extract (lane 1) compared with 2 samples from the early and mid proliferative phase (lanes 2,3) and from the luteal phase (lane 4 and 5; days 23 and 26, respectively) demonstrates a band at approximately 95 kD molecular weight, corresponding to β₃. Samples of endometrium were partially digested with collagenase and the glandular elements obtained (B) using a modification of the methods of Satyaswaroop et al., “Isolation and Culture of Human Endometrial Glands”, J. Clin. Endocr. Metab., 48:639-641 (1979). The glands appear as hollow structures free from surrounding stroma. Immunofluorescence of samples from lanes 3 and 4 (C and D, respectively) corresponds to the absence or presence of the 95 kD band in A. Magnification: 400×.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention is directed to methods of detecting receptivity of mammalian endometrium including obtaining a sample of endometrium, contacting the sample with a monoclonal antibody for the β₃ subunit of integrin and detecting the β₃ subunit.

For purposes of the present invention, the β₃ subunit may be β₃ alone or β₃ in combination with another integrin subunit, α_(v), for example.

As used herein integrin is defined as a diverse class of glycoprotein receptors expressed on the cell membrane. Integrins are cell adhesion molecules of the immunoglobulin superfamily. Integrins are composed of heterodimeric α and β subunits and are involved in cell—cell and cell—extracellular matrix adhesion. The integrin family is a broadly distributed group of receptors composed of noncovalently associated α/β heterodimer pairs that mediate leukocyte—leukocyte and leukocyte—endothelial cell adhesion, as well as cellular interactions with extracellular matrix components such as collagen, laminin, fibrinogen and fibronectin, and cell-cell interaction in organized tissues.

While integrins are found on virtually all cell types (the exception being red blood cells), expression of integrin subunits varies from cell type to cell type. In human uterine endometrium, as determined herein, glandular epithelial cells express primarily α₂, α₃ and α₆ integrin subunits, which are collagen laminin receptors. Stromal cells express predominantly α₅, a fibronectin receptor. The presence of α₁ on glandular epithelial cells is menstrual cycle specific, found only during the secretory phase. Expression of both subunits of the vitronectin receptor, α_(v)/β₃, also undergoes menstrual cycle specific changes on endometrial epithelial cells. The expression of α_(v) increases throughout the menstrual cycle while the β₃ subunit appears abruptly on menstrual cycle day 20 on luminal and glandular epithelial cells.

The present invention is directed to endometrium of the uterus of a mammal. The uterine wall is largely smooth muscle or myometrium. The endometrium, a glandular layer of variable thickness extremely sensitive to the hormones estrogen/progesterone, lines the myometrium. The endometrium is composed of several functional layers. The layer nearest the myometrium is termed the basalis layer, and the layer closer to the surface known as the functionalis. This tissue is made of epithelial cells, stromal (or mesenchymal) cells and endometrial leukocytes. The epithelial cells are either glandular (forming glands beneath the surface of the endometrium) or luminal (lining the surface of the endometrium). These different types of epithelium serve different purposes and staining patterns for different marker proteins are not always the same between glandular and luminal. It is the luminal surface that would encounter the human embryo first and is thought to be involved in initial attachment. The endometrium of premenopausal girls and postmenopausal women is atrophic due to the lack of the hormones, estrogen and progesterone. In the reproductive-aged woman, the endometrium undergoes cyclic developmental changes based on the ovarian cycle of hormone release. The first day of menstruation is the first day of the cycle; menstruation is generally completed by day 5. The endometrial growth then resumes under the influence of estrogen and progresses through the day 14, proliferative phase, and on to about day 28. From day 14 to day 28 the endometrium also shows signs of decreased gland growth and secretion, secretory phase, due largely to the influence of progesterone. During the follicular phase, while follicles are growing in the ovary, and estrogen is the dominant hormone, the endometrium grows thicker. With ovulation (typically day 14 of a 28 day cycle) the women is exposed to estrogen plus progesterone. This is called the secretory or luteal phase, and is noted for a stereotypic series of histologic changes that proceeds as the cycle continues. These histologic changes are used by pathologists to date the endometrium, a process that remains controversial despite its use for the past 40 years. There have been no reliable immunohistochemical markers reported that have proven utility in dating the endometrium.

Luteal phase dysfunction (LPD) is a term for developmental delay of the endometrium. It is a known cause of infertility, because of dysynchrony between the fertilized egg and the endometrium. If an embryo is ready to attach but the endometrium is delayed, then pregnancy is not likely to occur. The causes for LPD include inadequate hormonal output by the ovary, and may implicate defective signaling from higher centers such as inadequate gonadotropic hormone output from the pituitary or hypothalamus. LPD is a known cause of infertility and spontaneous abortion and can be corrected with hormone augmentation.

Embryo implantation stages include: apposition—when the epithelial cells of the embryo attach to the outer (luminal) epithelial cells of the maternal endometrial surface; adhesion; and invasion of trophoblast into the underlying stroma where it established itself and begins to grow. Contact with maternal blood vessels is made to gain nutrients and oxygenated blood and to rid itself of waste products during the invasion stage. The stage of development that the embryo reaches at the time of implantation is the blastocyst stage, which occurs at the same time as hatching. There is evidence that hatching is required before implantation occurs, perhaps because the embryo must have its epithelial cells exposed (out of the zona pellucida shell) to interact with the maternal cell layers. As set forth herein, this interaction occurs via integrins.

For purposes of the current invention, mammals include, but are not limited to the Order Rodentia, such as mice; Order Logomorpha, such as rabbits; more particularly the Order Carnivora, including Felines (cats) and Canines (dogs); even more particularly the Order Artiodactyla, Bovines (cows) and Suines (pigs); and the Order Perissodactyla, including Equines (horses); and most particularly the Order Primates, Ceboids and Simoids (monkeys) and Anthropoids (humans and apes). The mammals of most preferred embodiments are humans.

Monoclonal antibodies useful in the practice of the invention include any monoclonal antibodies having an affinity to or binding to the β₃ subunit of integrin. An example of such a monoclonal antibody is SSA6. Monoclonal antibody SSA6 may be produced as described by Bennett et al., PNAS, Vol. 80, 2417-2421 (1983).

Monoclonal antibodies which recognize β₃ combined with another integrin subunit may also be used. One such monoclonal antibody is 23C6, which may be prepared according to the method of Davies et al., J. Cell Biol., Vol. 109, 1817-1826 (1989). Immunostaining with monoclonal antibodies such as 23C6 (specific to the intact α_(v)/β₃ integrin, i.e. the vitronectin receptor) produces the identical pattern as SSA6 which only measures the β₃ subunit. This demonstrates that while α_(v) specific antibodies measure all the α_(v) containing integrins, antibodies which recognize the intact α_(v)/β₃ integrin or the β₃ subunit can be used to study this integrin (the α_(v)/β₃ “vitronectin receptor”).

Other monoclonal antibodies can be used. The preparation of monoclonal antibodies is known to those in the art. Particularly, the method of Kohler and Milstein, Nature, 256: 495-497 (1975) may be used to produce monoclonal antibodies for use in the invention.

Methods of obtaining endometrial tissue samples for analysis, include any surgical and nonsurgical technique known in the art. Surgical methods include, but are not limited to biopsy, dilation and curettage. Nonsurgical methods include, but are not limited to, uterine washings and uterine brushings with immunocytochemical evaluation.

Methods of detecting β₃ in the endometrium include all methods of identifying glycoproteins known in the art. These methods include, but are not limited to, immunohistochemistry techniques such as immunoblotting or Western blotting, immunoperoxidase staining, fluorescein labeling, diaminobenzadine and biotinylation.

Generally, immunohistochemistry involves staining cryosectioned tissue samples. As used herein, endometrium samples may be cryosectioned to about 4-8 μ thick. Endometrium is contacted with primary antibody, such as SSA6, followed by contact with secondary antibody, such as biotinylated goat anti-mouse antibody. Endometrium is then incubated in avidin-conjugated horseradish peroxidase macromolecular complex followed by chromogen incubation, such as diaminobenzadine. Fluorescein may then be added to observe integrin distribution.

Immunoblotting involves the analysis of protein, here integrin, on sodium dodecylsulfate-polyacrylamide gel electrophoresis SDS-PAGE. The gel is run under nonreducing conditions and the samples are transferred to a nitrocellulose membrane for example. The membrane is incubated in media containing primary antibody, such as SSA6. The filter is developed using a secondary antibody, such as alkaline phosphatase-conjugated goat anti-mouse antibody.

The methods of diagnosing infertility and for detecting the window for embryo implantation in the endometrium of a mammal are also within the scope of the invention. As provided herein, the β₃ subunit of integrin appears at day 20 of the menstrual cycle. It is also provided herein that α_(v)/β₃ on endometrial epithelium binds fibronectin, vitronectin and osteopontin. These molecules may provide a bridge between the α_(v)/β₃ integrin of the endometrium and the embryo. Further, patients with luteal phase dysfunction have delayed endometrial maturation, infertility and negative staining for β₃ on days 20 through 24. Thus, the optimal time for fertility may be determined by repetitively testing endometrial samples at a plurality of stages in the menstrual cycle. As such, screening for β₃ provides a method of diagnosing infertility and for detecting the window of embryo implantation in the endometrium. The window of implantation is that time when the endometrium of the uterus is available for embryo implantation. This window is preferably from day 19 to day 23, and more preferably day 20 of the human menstrual cycle, marked by the expression of α_(v)/β₃ integrin.

Similar cycles are known for other mammals—it is within the ordinary skill in the art to adopt the foregoing methodology to such cycles.

The present invention is also directed to methods of in vitro fertilization. Once the β₃ subunit of integrin is detected in an animal selected for pregnancy, a fertilizable egg (or eggs) from the same or different animal could be replaced into the uterus to establish pregnancy. The egg and appropriate sperm are combined to produce a zygote in vitro. For purposes of the invention, in vitro fertilization may take place in a petri dish, in a test tube or the like. In addition, in vitro fertilization may also refer to independently adding eggs and sperm to the fallopian tubes such that the zygote is formed therein. In any event, the zygote is introduced to the uterus of the animal selected for pregnancy and monitored for implantation into the endometrium of the uterine wall.

Alternatively, the invention is directed to methods of preventing embryo implantation. Such may be carried out by contacting the endometrium with a neutralizing Fab fragment specific for β₃. For purposes of the present invention, Fab fragments from monoclonal antibodies which bind β₃ are within the scope of the invention. Fab fragments include, but are not limited to, Fab fragments from monoclonal antibodies SSA6 and 23C6. The Fab fragment may remain in vivo for a therapeutically effective time to prevent embryo implantation. The Fab fragment comprises the ligand binding portion of a monoclonal antibody for β₃, i.e. the binding site for β₃. A neutralized Fab fragment is used in place of a typical monoclonal antibody to reduce the possibility of an inflammatory reaction.

Contraception is a further embodiment of the invention. A contraceptive may include a therapeutically effective amount of neutralizing Fab fragment monoclonal antibodies specific for β₃ in a pharmaceutically acceptable carrier, preferably adapted for intrauterine application.

Compounds which specifically block binding of the embryo to this α_(v)/β₃ receptor are also included within the scope of the present invention. Examples include peptides containing the amino acid sequence arginine-glycine-aspartic acid, RGD (Pierschbacher et at., “Synthetic Peptide with Cell Attachment Activity of Fibronectin”, PNAS, Vol. 80, 1224-1227 (1983)) which is the active binding site for the vitronectin receptor. This sequence has been reported to block attachment of pregnancy derived cells (trophoblast) in vitro by researchers, Kao et al., “The Human Villous Cytotrophoblast: Interactions with Extracellular Matrix Proteins, Endocrine Function, and Cytoplasmic Differentiation in the Absence of Syncytium Formation”, Development, Vol. 130, 693-702 (1988). Thus, a contraceptive containing the sequence RGD may be administered locally to prevent embryo implantation.

Pharmaceutically acceptable carriers include, and are not limited to, vaginal suppositories, intrauterine devices (IUD), gels such as slow release formulation, for example, depo forms of hormones—microcrystals injected and slowly released into the systemic circulation or delivered in silastic tubing. Contraceptive formulations would be administered in about 10 μg/ml.

Methods of monitoring endometrial maturation is also within the scope of the present invention. The endometrium may be monitored for embryo receptivity, embryo implantation, infertility, endometrial replenishment and ovulation.

Diagnostic kits are also within the scope of this invention. Such kits include monoclonal antibodies to rapidly detect β₃ in solution; an absorbant detection device which contains pre-absorbed antibody against β₃ and to which uterine washings can be applied; a developer to make β₃ visible when present.

The present invention is further described in the following examples. These examples are not to be construed as limiting the scope of the appended claims.

EXAMPLES

Human Samples

Endometrium was obtained from 35 reproductive age women at the time of hysterectomy. Tissue was obtained from the early proliferative (day 5) through late secretory phase (day 28) and all hysterectomies were performed for benign disease. Endometrial biopsies were performed on women as part of their evaluation for infertility. All patients were cycling normally and none had received hormones for at least 3 months prior to surgery. Dating of the endometrium was assessed according to the criteria of Noyes et al., “Dating the Endometrium” Fertil. Steril., 1:3-8 (1950). Endometrial biopsies were evaluated in the context of timing of ovulation and/or the onset of the next menstrual period. Samples were judged as “out of phase” if histologic dating was delayed by 3 or more days relative to the predicted day of the menstrual cycle. Proliferative endometrium was categorized based on histology and on last menstrual period. Samples were transported on ice to the laboratory and were snap frozen on dry ice and stored at −70° C.

Antibodies

Monoclonal antibodies (Mabs) PIH5, PIB5, PID6 specific to α₂, α₃, α₅ subunits, respectively, were acquired from Drs. Elizabeth Wayner and William Carter. Mabs TS2/7 and B-5H10 directed against the α₁ and α₄ subunits, respectively were acquired from Dr. Martin Hemler. GoH3, a specific Mab directed against α₆ was acquired from Dr. Arnoud Sonnenberg. Mab SSA6 specific to the β₃ subunit was acquired from Drs. Joel Bennett and James Hoxie. Mab LM142 against α_(v) was acquired from Dr. David Cheresh. The β₄ antibody was acquired from Dr. Steven Kennel. The 23C6 antibody which recognizes β₃ attached to α_(v) was obtained from Michael Horton.

Immunohistochemistry

Immunoperoxidase staining was performed on cryostat sections of endometrium samples from throughout the menstrual cycle. Serial cryosections 4-8 μ thick were placed onto poly-L lysine coated slides, fixed in −20° C. acetone for 10 minutes, and stained using Vectastain Elite® ABC kits (Vector Laboratories, Burlingame, Calif.). Diaminobenzidine (DAB; Sigma Chemical Co., St. Louis, Mo.) was used as the chromogen. Primary antibody was placed on cryosections following blocking with 1% bovine serum albumin in PBS, and allowed to bind at room temperature for 1 hour. A phosphate buffered saline (PBS) pH 7.2 to 7.4 rinse was followed by secondary antibody consisting of biotinylated goat anti-mouse antibody for 30 minutes. Following a PBS rinse, the endogenous peroxidases were quenched with a 30 minute incubation with 0.3% H₂O₂ in absolute ethanol, followed by a 30 minute rehydration in PBS. Avidin:biotinylated horseradish peroxidase macromolecular complex (ABC) was then incubated on the sections for 30 minutes before adding diaminobenzadine for 3 minutes to complete the reaction. Some samples were treated with 1:200 dilution of fluorescein-labeled anti-mouse antibodies for 1 hr., for immunofluorescent microscopy. Samples were subsequently washed in PBS and mounted. The resulting staining was evaluated on a Nikon microscope at low (100×) and higher (400>) magnification with or without fluorescence. Staining was judged as absent (−), weak (±), moderate (+) or strong (++). Examples of each is presented in FIG. 3. Photomicrographs were made using Kodak T-MAX 100 ASA film.

Integrin Distribution in Normal Endothelium

The distribution of α₂, α₃, α₆, and β₄ subunits of integrins which recognize primarily collagen (Col) and/or laminin (LM) is shown in FIGS. 1A-D. These subunits were present on glandular epithelium (←) throughout the menstrual cycle. Their distribution within the endometrium was typical of that seen for most epithelial tissues. The α₂ and α₃ subunits were distributed around the entire circumference of the cells, while the α₆ and β₄ subunits appeared to be localized at the basolateral surface, adjacent to the basement membrane (BM) of the endometrial glands. The expression of these subunits by the mesenchyme (*) was less pronounced. While moderate staining was seen for α₆ on stromal cells (FIG. 1C) very little staining was noted for β₄. The expression of the α₄ and α₅ subunits of integrins known to bind fibronectin (Table 1) was quite restricted. The α₄ subunit was undetectable above background staining (compare FIG. 1 E with FIG. 2C) in either epithelium or mesenchyme. The α₅ subunit (FIG. 1F), representative of the classic fibronectin receptor was not seen on the epithelial components, but was strongly expressed in the mesenchyme which is rich in fibronectin.

TABLE 1 DISTRIBUTION OF INTEGRINS BY LIGAND SPECIFICITY Ligands Integrin subunit Collagen/Laminin Fibronectin/Vitronectin α₁/β₁ α₄/β₁ α₃/β₁ α_(v)/β₁ α₂/β₁ α₅/β₁ α₆/β₁ α_(v)/β₃ α₆/β₁ α₆/β₄

The intensity of immunostaining for three other subunits of integrins was found to change in a menstrual cycle-dependent manner. Immunostaining for α₁ in the proliferative phase (FIG. 2A) was only slightly above background levels (FIG. 2C). The intensity of staining increased throughout the secretory phase (FIG. 2B). This intense circumferential staining was found on glandular and luminal epithelium on all samples from day 15 to 28. Likewise, α_(v) was weakly expressed on both the epithelium and mesenchyme in the proliferative phase (FIG. 3A) and staining increased gradually during the secretory phase to the level noted in FIG. 3B. During the proliferative phase β₃ staining was only present on the mesenchymal cells (FIG. 3C). Increased β₃ staining was apparent on the endometrial epithelium only after day 19 of the menstrual cycle (FIG. 3D) on the luminal as well as glandular epithelium, and was also present in a pericellular distribution. In contrast, the basalis layer did not significantly stain for either α_(v) or β₃. This changing pattern of epithelial α_(v) and β₃ throughout the cycle was studied in 35 endometrial samples and is depicted graphically in FIGS. 4A and B.

Collagen/laminin receptors (col/LM) characterized by α₂, α₃ and α₆ were uniformly expressed throughout the menstrual cycle, see Table 2. The pericellular distribution of α₂ and α₃ subunits was distinctly different from that of α₆ subunit. Characteristic of a laminin receptor, α₆ was concentrated on the basolateral surface. The β₄ subunit which pairs with α₆, was also found distributed on the basolateral surface of epithelial cells, and its distribution appeared even more restricted to the basal pole. The α₅/β₁ integrin, a major fibronectin receptor, was also uniformly expressed throughout the menstrual cycle. Unlike the collagen and laminin receptors, the distribution of α₅/β₁ was limited to the mesenchyme.

The temporal pattern of distribution of α_(v) was varied. Immunostaining was first detected prior to the secretory phase with an increase in intensity throughout the cycle. One subunit known to pair with α_(v) is β₃. β₃ is not characteristically present on epithelial cells. The abrupt appearance of the β₃ subunit after day 19 suggests that expression of the vitronectin receptor is regulated in human endometrium. The increased epithelial α_(v)/β₃ staining in normal cycles correlates to an implantation window within the secretory phase. While the physiologic basis for the implantation window has not been previously established, a proposed role of integrins in the initial interaction between maternal and embryonic cells indicates an endometrial period of receptivity.

TABLE 2 DISTRIBUTION OF INTEGRIN SUBUNITS IN NORMAL ENDOMETRIUM DURING THE MENSTRUAL CYCLE Col/LM FN/VN Cell Type α₁ α₂ α₃ α₆ β₄ α₄ α₅ α_(v) β₃ Epithelial ∘ • • •^(b) •^(b) ∘ ∘ ∘ ∘ proliferative early secretory • • • • • ∘ ∘ * ∘ late secretory • • • • • ∘ ∘ • • Stromal proliferative ∘ ∘ ∘ • ∘ ∘ • • • early secretory ∘ ∘ ∘ * ∘ ∘ * • • late secretory * ∘ ∘ • ∘ ∘ * • • ^(b)= basolateral distribution of staining • = + or ++ staining * = ± staining ∘ = − staining Integrins in Discordant Endometrium.

The presence of the epithelial β₃ subunit appeared to be a consistent internal marker of luteal phase maturation, and the timing of β₃ expression correlated with the peri-implantation period or window of embryo implantation. To investigate whether this phenomenon would be useful in the clinical evaluation of endometrial biopsies, immunostaining was performed on luteal phase endometrial samples from cycles which showed evidence of maturational delay. Endometrial biopsies from 25 women who had concordance of menstrual and histologic dating (“Normal” group) were compared to 12 biopsies which were identified as ≧3 days out of phase (OOP) based on either the time of ovulatory or the subsequent menses. Samples were immunostained for α₁, α_(v) and β₃ subunits. All biopsies were performed on days 20 to 24 of the menstrual cycle. In all instances, immunostaining for these three antigens was present on endometrial epithelia from the normal group. In biopsies which were delayed by 3 days or more, α₁ and α_(v) staining was present, but epithelial β₃ staining was absent. The comparison of β₃ staining intensity in the two groups is shown in FIG. 5A. Accompanying photomicrographs of β₃ immunostaining from out of phase biopsies (OOP; B) and normal “in phase” biopsies (C) is included, which demonstrates the discrepancy seen in β₃ staining. In subsequent treatment cycles, 2 OOP patients underwent repeat biopsy during a normalized cycle at which time immunostaining for epithelial β₃ was present. This suggests that the lack of β₃ was not an intrinsic defect in the OOP group. Rather, the discordant biopsies which lacked β₃ had not yet established the mid-luteal phenotype of normal day 20 to 24 endometrium.

Cell Harvest and NP-40 Extraction

To further demonstrate that immunohistochemical staining accurately reflected changes in the expression of β₃ subunit on endometrial epithelium, immunoblots (Western blots) were performed on samples of enriched endometrial glandular elements from proliferative and secretory phase. Four samples of endometrium were obtained for the evaluation of the β₃ subunit in proliferative (n=2) and late secretory (n =2) endometrial epithelium. Each sample was placed in Dulbecco's modified Eagle's medium (DMEM; Sigma, St. Louis, Mo.), supplemented with 10% fetal bovine serum (Flow Laboratories, McLean, Va.) glucose (4500 mg/L), Hepes buffer (25 mM), L-glutamine (584 mg/L), and sodium bicarbonate (3.7 gms/L). Endometrium was minced in a plastic petri dish prior to incubation with 6 mg of collagenase (type 1A, 550 units/mg; Sigma, St Louis, Mo.) for 2 hours at 37° C. utilizing modifications of the procedures described by Satyaswaroop et al. in “Isolation and Culture of Human Endometrial Glands”, J Clin. Endocr. Metab., 48:639-641 (1979). The resulting suspension was successively passed through a 250 μm sieve and a 38 μm seive (Newark Wire Cloth Co, Newark N.J.). The course (250 μm) sieve removed undigested material, while the second retained the glandular elements and excluded the individual stromal and blood cells. After thorough rinsing, the glandular elements were obtained by backwashing with 10 to 20 ml of DMEM. The isolated glandular structures were then transferred to a 1.5 ml microfuge tube and centrifuged 3 times (82×g) for 2 minutes with intermittent washes with PBS. Membrane extracts were prepared by adding small volumes (100-200 μl) of 10 mM Tris-acetate, pH 8.0, 0.5% NP-40, 0.5 mM Ca²⁺ (TNC) with 2 mM PMSF (phenyl methyl-sulfonyl fluoride) to the final pellet, pipetted and incubated on ice for 15 minutes. The lysate was centrifuged for 5 minutes at 16,000×g in a microcentrifuge. The resulting supernatant was called NP-40 extract and was frozen at −70° C. until use. A portion of the original, undigested tissue was cryosectioned for immunohistochemical localization of β₃.

Gel Electrophoresis and Immunoblots

The protein concentration of each NP-40 extract and an extract of platelets (positive control) was determined using technique described by Lowry et al., “Protein Measurement with Folin Phenol Reagent”, J. Biol. Chem., 193:265-271 (1951). Samples with equal amounts of protein were added to electrophoresis sample buffer (62.5 mM Tris base, 2% SDS, 10% glycerol, pH 6.8). Samples were analyzed by SDS-PAGE using 6% polyacrylamide gels, using non-reducing conditions described by Laemmli, U.K., “Cleavage of Structural Proteins During Assembly of the Head of Bacteriophage T4”, Nature, 227:680-685 (1970). The gel was transferred to nitrocellulose using a Biorad transfer apparatus (Biorad, Richmond, Calif.) and blocked with 4% BSA in PBS with 0.2% Na Azide for 1 hour. After addition of primary antibody (SSA6 supernatant) for 2 hours, the gels were developed using an alkaline phosphatase-conjugated secondary antibody (Promega Corp., Madison, Wis.) according to methods described by Albelda et al., “EndoCAM:A Novel Endothelial Cell-Cell Adhesion Molecule”, J. Cell Biol., 110:1227-1237 (1990).

As shown in FIG. 6A, proliferative phase epithelial structures had little to no immunostaining at 95 kD (lanes 2 and 3), compared to the positive control (platelet extract; lane 1) or to samples from the secretory phase (lanes 4 and 5) which showed strong staining for β₃. The isolated endometrial glands appeared as tubular structures free of surrounding stroma (FIG. 6B). Immunofluorescent staining for β₃ from samples corresponding to lanes 3 and 4 (mid proliferative phase and day 23, respectively) are shown in FIGS. 6C and D. Note the absence of glandular staining in the proliferative sample, while both glandular and luminal immunostaining is obvious from the secretory phase. These data confirm that the expression of epithelial β₃ in human endometrium is a cycle specific phenomenon.

Various modifications of the invention in addition to those shown and described herein will be apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims. 

1. A method for detecting receptivity of the endometrium of a mammal to embryo implantation, comprising the steps of: a) detecting β₃ integrin subunit in an endometrial sample from the mammal; and b) correlating the presence of the β₃ integrin subunit with endometrial receptivity.
 2. The method of claim 1, wherein the sample of endometrium is obtained surgically.
 3. The method of claim 2, wherein the sample is obtained by a biopsy or by a dilation and curettage.
 4. The method of claim 1, wherein the sample of endometrium is obtained nonsurgically.
 5. The method of claim 4, wherein the sample is obtained by a uterine washing or by a uterine brushing.
 6. The method of claim 1, wherein the β₃ subunit is combined with another integrin subunit.
 7. A method of monitoring endometrial maturation in a mammal, comprising: a) detecting the appearance of the β₃ subunit of integrin in a sample of endometrium obtained from the mammal at a plurality of stages of the endometrial cycle; and b) correlating the appearance of the β₃ subunit of integrin with endometrial maturation.
 8. The method of claim 7, wherein the appearance of β₃ is monitored on days 19-23 of the menstrual cycle.
 9. The method of claim 7, wherein the appearance of β₃ is monitored on days 20 to 24 of the menstrual cycle.
 10. The method of claim 7, wherein delayed maturation is indicative of infertility.
 11. The method of claim 7, wherein the β₃ subunit is combined with another integrin subunit.
 12. A method of detecting the window of embryo implantation in endometrium in a mammal, comprising: a) detecting the presence of a β₃ integrin subunit in endometrium samples obtained from the mammal at a plurality of stages of the menstrual cycle; and b) correlating the presence of β₃ with the window of embryo implantation.
 13. The method of claim 12, wherein the sample of endometrium is obtained surgically.
 14. The method of claim 13, wherein the sample is obtained by a biopsy or by a dilation and curettage.
 15. The method of claim 12, wherein the sample of endometrium is obtained nonsurgically. 